This invention relates to the field of power supplies or power converters and more particularly to on-line, isolated solid state sources with battery back up in which the input, the output, and battery voltages are significantly different.
FIGS. 1 and 2 show related designs of isolated un-interruptible power supplies with battery back up in which two transformers are used to achieve isolation. In the circuit of FIG. 1, ac input voltage from an external mains source is rectified by a function represented by the FIRST CONVERTER BRIDGE RECTIFIER block and filtered by a function represented by the FIRST L/F FILTER block, a low frequency filter. A first high frequency inverter represented by the FIRST H/F INVERTER block uses a first transformer T1 to provide power via a high frequency rectifier represented by a H/F RECTIFIER block and H/F FILTER to a battery charging bus identified as BATT. A low frequency inverter represented by the L/F INVERTER block uses a second transformer T2 to provide sinusoidal power to the load via a second low frequency filter represented by SECOND L/F FILTER block. The second transformer T2 provides galvanic isolation from the load to the battery and the low frequency inverter. Since the output power from the second transformer T2 is at the output line frequency of 50-60 Hz, the second transformer is large and heavy.
The isolated un-interruptible power supply of FIG. 2 uses a first high frequency inverter represented by the H/F INVERTER block to drive a first transformer T3. The secondary of transformer T3 provides power via the FIRST H/F RECTIFIER and H/F FILTER blocks to a battery charging buss designated by the legend BATT. Power is provided from the BATT buss to a second high frequency inverter represented by the SECOND H/F INVERTER block. The battery clamps or limits the voltage on the BATT buss. The secondary of T4 drives a high frequency rectifier and filter to provide one or more high voltage rails. Transformer T4 is a small and light high frequency component.
The function represented by the L/F INVERTER block of FIG. 2 produces a 60 Hz output source of power using a solid state dc-to-ac drive. The L/F INVERTER provides the 60 Hz output by pulse width modulating power off the dc rails from the H/F RECTIFIER and FILTER, through an inductor within the L/F INVERTER. The function represented by the L/F INVERTER block copies the required sinusoidal waveform without regard to the current required, subject to the instantaneous current required at any time remaining within predetermined limits.
The circuit of FIG. 2 offers a saving over the circuit of FIG. 1 in that the first circuit uses a low frequency second transformer T2 and the circuit of FIG. 2 uses a high frequency second transformer T4 which would be smaller and lighter for an equivalent power output capability. Both circuits have a low frequency inverter which has at least one inductor (not shown).
Some on-line sources use a larger stack of batteries to form a high voltage battery bus to eliminate the need for a separate boost section to boost the battery stack voltage up Some on-line sources use a larger stack of batteries to form a high voltage battery bus to eliminate the need for a separate boost section to boost the battery stack voltage up to the dc rail voltages which might be +/xe2x88x92200 Vdc. The battery voltage can be directly used to feed the critical load. However, a smaller battery stack with a lower battery bus voltage, i.e. 48 Vdc. The lower battery bus is believed to be preferred because a battery stack with fewer cell s in series is believed to be more reliable and more easily maintained.
The systems of FIGS. 1 and 2 are continuous on-line system that keeps the batteries connected while operating, and pass the total power consumed including battery charging power, through the first transformer T1 or T3. Load power alone flows through the second transformer T2, or T4. The combined power, passing through the T1 or T3 transformer, increases the required power rating for the first transformer. The volume of the two input transformers as well as their size and weight exceed the volume, size and weight of the single transformer required for the single transformer used in the subject invention.
The invention, UN-INTERRUPTIBLE POWER SUPPLY(UPS) reduces the system cost, volume, and weight by using a single three winding high frequency power transformer instead of the two transformers used by conventional systems. Input, output and battery sections are respectively connected via the three power windings of the high frequency transformer isolating the sections from each other and establishing galvanic isolation between the output load and the input power source.
FIG. 3 shows the invention un-interruptible power supply within phantom block 10. 50-60 Hz ac Mains power from voltage source 12 is applied at input terminals 14 of I/P FILTER (input power filter) 16. The I/P FILTER 16 filters and passes the power to rectifier 18 providing unregulated and unfiltered dc voltage to a low-pass filter 20. The output of the low-pass filter 20 is an unregulated dc source 22 that is coupled to the input 24 of the INPUT INVERTER 26 which typically uses an H-Bridge inverter circuit to drive the primary winding N1 of transformer T5. The combination of elements within phantom box 28 is represented as a dc voltage source 22 at input inverter input 24 in FIGS. 4, 5 and 6.